1. Field of the Invention
The present invention relates to methods of conducting catalytic chemical reactions under conditions so as to minimize or substantially avoid deactivation of the catalyst material due to a reaction of dialkyl sulfides with the catalyst material. More particularly, the present invention relates to the preparation of alkyl tertiary alkyl ether by catalytic reaction of hydrocarbon streams containing mixtures of isoolefins and alcohols under conditions which minimize or substantially avoid reaction of the catalytic material in the catalytic reaction zone with any dialkyl sulfides which may be present in the stream. Specifically, the present invention is directed to a catalytic reaction for producing alkyl tertiary alkyl ether which involves removing dialkyl sulfides from the hydrocarbon stream prior to introduction of the stream into the catalytic reaction zone and/or introducing sufficient amounts of oxygenates to the reaction zone to inhibit reaction of dialkyl sulfides which may be present in the stream with the catalyst material.
2. Discussion of Background and Material Information
Methyl tertiary butyl ether (MTBE) in recent years has become an important product of the petroleum industry in view of its acceptance as a non-environmentally harmful octane improver for gasolines.
In view of the octane improving characteristics of MTBE, processes, such as those disclosed in U.S. Pat. Nos. 3,726,942 and 3,846,008, have been developed to separate isoolefins, and isobutene in particular, from mixtures with corresponding normal olefins and alkanes which involves etherifying the isoolefins with a C.sub.1 to C.sub.6 primary alcohol in the presence of an acidic cation exchange resin catalyst followed by fractionation to separate the low boiling hydrocarbons from the higher boiling ether.
In a variation of these processes, as described in U.S. Pat. Nos. 3,629,478 and 3,634,534, HAUNSCHILD, the mixture of isoolefin and normal olefin with lower primary alcohols is fed to a distillation column in which there are a plurality of zones of acidic ion exchanges resin catalysts whereby the isoolefin ether is formed and drops to the bottom of the column while normal olefins, and paraffins, are distilled overhead.
More recently, catalytic distillation processes, such as those disclosed in U.S. Pat. Nos. 4,232,177, 4,307,254, and 4,336,407, SMITH, Jr., have been developed to improve the recovery of MTBE.
For example, U.S. Pat. No. 4,232,177, SMITH, Jr., is broadly directed to a method for concurrently conducting chemical reactions to produce a reaction mixture and fractionation of the reaction mixture which involves feeding reactants to a distillation column reactor into a feed zone. The reactants are then contacted with a fixed bed catalyst packing in a distillation-reaction zone, thereby catalytically reacting the reactants to form a reactant mixture. The reactant mixture is then fractionated in the fixed bed catalyst to recover a lower boiling fraction of the reaction mixture overhead and a higher boiling fraction as a bottom, whereby the reaction and fractionation occur concurrently in the fixed catalyst bed which serves as both catalyst and distillation packing in the distillation column reactor. It is disclosed that this method is particularly suitable for producing methyl tertiary butyl ether wherein the reactants include isobutene and methanol which is disclosed as preferably being present in a stoichiometric amount, although it is speculated that an excess of up to 10% of stoichiometric may be desirable.
U.S. Pat. No. 4,447,668, SMITH, Jr., is directed to disassociation of alkyl tertiary butyl ethers by vapor phase contact with a cation acidic exchange resin to produce a stream consisting of unreacted ether, isobutene, and an alcohol corresponding to the alkyl radicals.
U.S. Pat. Nos. 4,215,001 and 4,250,052, SMITH, Jr., are directed to a catalyst system and a catalyst structure, respectively, for separating isobutene from C.sub.4 stream, respectively.
U.S. Pat. No. 4,375,576, SMITH, Jr., is directed to a liquid phase reaction of isobutene in the presence of resin cation exchange resins.
U.S. Pat. No. 4,242,530, SMITH, Jr., is directed to a method for the separation of isobutene from a mixture of n-butene and isobutene which involves feeding a C.sub.4 stream containing isobutene to a distillation column reactor into a feed zone, contacting the stream with fixed bed acidic cation exchange resin to form diisobutene which passes to the bottom of the column and is removed.
U.S. Pat. No. 4,302,356, SMITH, Jr., is directed to a catalyst system for use in a reaction-distillation column which is a cloth belt having a plurality of pockets containing acid cation exchange resin arranged and supported by wire mesh intimately associated with the cloth pockets, particularly by pulling the cloth belt with the wire mesh disposed between the coils, i.e., in a spiral.
U.S. Pat. No. 4,071,567, ANCILLOTTI et al., is directed to a process for preparing methyl tert-butyl ether by reacting methanol with isobutene in the presence of an acid ion exchange resin in two stages by feeding the methanol and isobutene mixed with other hydrocarbons to respective members of a pair of interconnecting reactors so that the quantity of alcohol present in one of the reactors is in excess of the stoichiometric equivalent of the quantity of isobutene therein, while the quantity of isobutene present in the other reactor is in excess of the stoichiometric equivalent of the quantity of methanol therein, and the methyl tert-butyl ether so formed is recovered through distillation.
U.S. Pat. No. 4,254,296, MANARA et al., is directed to a process for preparing tertiary olefins from tertiary alkyl ethers, such as methyl tert-butyl ether which involves using a catalyst system which consists of a crystalline silica having a high specific surface area and which has been modified by an oxide of a metallic cation having at least partially amphoteric character.
U.S. Pat. No. 4,475,005, PARET, is directed to a process for preparing tertiary alkyl ethers from isoolefins and aliphatic alcohols in the presence of a catalyst characterized in that the reaction leading to the formation of the tert-alkyl ether and the separation of the tert-alkyl ether from the hydrocarbons and compounds which accompany it takes place in a single plate fractionating apparatus.
Notwithstanding the recent attempts to improve the production of isobutene and MTBE, a problem associated with conventional processes for the production of MTBE is that the catalyst material used in the catalyst reaction processes has a tendency to deactivate in an unacceptably short period of time.